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    <title>Document</title>
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<body>
    <script>
        var a=new Array(3);
        var b=[undefined,undefined,undefined];
        var c=[null,null,null];
        var d=[false,false,false];
        var e=[0,0,0];
        console.log(a.join('-'));//--
        console.log(b.join('-'));//--
        console.log(c.join('-'));//--
        console.log(d.join('-'));//false-false-false
        console.log(e.join('-'));//0-0-0
        //数组的 join() 方法将数组中的所有元素连接成一个字符串
    </script>
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